MYB proteins are a group of transcription factors. The cellular myb proto-oncogene (c-myb) is involved in the proliferation and/or differentiation of haematopoietic cells (Graf (1992) Curr. Op. Gen. Devel. 2, 249-255). Common to all MYB gene products is a strongly conserved DNA-binding domain located at the N-terminal end. In animals, this DNA-binding domain consists of three imperfect repeats of approximately 51-52 amino acids each (designated R1, R2, and R3) with three highly conserved tryptophan residues regularly spaced by 18 or 19 amino acids (Weston (1999) Curr. Op. Gene Devel. 8, 76-81). In plants and yeast, the predominant MYB proteins have two repeats (R2 and R3) (Martin and Paz-Ares (1997) Trends Genet. 13, 67-73; Jin and Martin (1999) Plant Mol. Biol. 41, 577-585). However, MYB proteins containing only one repeat or three repeats have also been identified in plants (Baranowskij, et al. (1994) EMBO J 13, 5383-5392; Kirik and Bäumlein (1996) Gene 183, 109-113; Feldbrügge, et al. (1997) Plant J. 11, 1079-1093; Wang, et al. (1997) Plant Cell 9, 491-507; Braun and Grotewold (1999) Plant Physiol. 121, 21-24).